1. Field of the Invention
The present invention relates to a stepping motor control circuit, a movement provided with the stepping motor control circuit, and an analog electronic timepiece using the movement.
2. Background Art
In the related art, a stepping motor, which is provided with a stator having a rotor accommodation through-hole and a plurality of positioning units that determine a stable stationary position of a rotor, the rotor being disposed inside the rotor accommodation through-hole, and a drive coil being wound around the stator, has been used in an analog electronic timepiece and the like. To allow the stepping motor to rotate in a relatively reliable manner, rotation detection thereof is carried out to allow the stepping motor to operate according to rotation detection results (for example, refer to Japanese Patent Nos. 3302804 and 4165092, International Publication No. 2005/119377, and JP-A-2010-166798).
A rotation detection method described in Japanese Patent Nos. 3302804 and 4165092 is configured to have a first detection section in which a rotor movement state after blocking a drive pulse is detected, and a second detection section in which an induced signal in a direction opposite to that of the first detection section is detected to carry out the final rotation determination based on the result. According to this configuration, rotation detection of the stepping motor is carried out, and the stepping motor is allowed to rotatably drive by the drive pulse according to rotation detection results.
The rotation detection is possible by the configuration. However, there is a problem in that in a case where a load variation (a calendar load, or a load of a moment of the long hand) is large, an induced signal varies, and thus accurate rotation detection is difficult.
On the other hand, a rotation detection method described in International Publication No. 2005/119377 is configured as follows. After rotating a rotor with a main drive pulse P11, when a detection voltage of an induced signal is less than a reference voltage Vcomp, the rotor is driven with a correction drive pulse P2, and the rotor is driven after changing (pulse-up) a next main drive pulse P1 to a main drive pulse P12 having energy larger than that of the main drive pulse P11. In addition, when it is detected that a detection time during rotation with the main drive pulse P12 is faster than a reference time, the main drive pulse P12 is pulsed down to the main drive pulse P11 to allow the rotor to drive with an appropriate main drive pulse P1.
However, the detection method is a rotation detection method using a phenomenon in which a detection time of the induced signal is delayed along with a relative load increase with respect to the drive energy, and a level of the induced signal decreases. Accordingly, when a load variation (a calendar load, or a load of a moment of the long hand) which is equal to or more than a certain load variation occurs, an angular velocity of the rotor decreases, and thus the induced signal is apt to decrease regardless of rotation. Therefore, there is a problem in that rotation is falsely detected as non-rotation, and thus the rotor is driven with the correction drive pulse. As a result, there is a problem in that a consumption current increases, and the lifetime of a battery decreases.
In addition, the rotation detection method described in JP-A-2010-166798 is a rotation detection method using a phenomenon in which the detection time of the induced signal is delayed along with an increase in a load, and a pattern of an induced signal VRs in sections obtained by dividing a detection section into a plurality of sections is different depending on a rotation state of the stepping motor. However, similarly to the invention described in International Publication No. 2005/119377, there is a problem in that false rotation detection may be conducted due to an effect of a load variation, and power consumption may increase.